1. Field of the Invention
The present invention relates to an electron emission device. In particular, the present invention relates to an electron emission device having a spacer loading region, in which the width of the spacer loading region is defined to reduce the deterioration of screen image quality due to charging of spacers.
2. Description of Related Art
Generally, electron emission devices are classified into those using hot cathodes as the electron emission source, and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type and a surface conduction emitter (SCE) type.
The MIM type and the MIS type electron emission devices have electron emission regions with a metal/insulator/metal (MIM) structure and a metal/insulator/semiconductor (MIS) structure, respectively. When voltages are applied to the two metals, or the metal and the semiconductor, on either side of the insulator, electrons migrate from the high electric potential metal or semiconductor to the low electric potential metal, where the electrons are accumulated and emitted.
The SCE type electron emission device includes a thin conductive film formed between first and second electrodes arranged facing each other on a substrate. High resistance electron emission regions or micro-crack electron emission regions are positioned on the thin conductive film. When voltages are applied to the first and second electrodes and an electric current is applied to the surface of the conductive film, electrons are emitted from the electron emission regions.
The FEA type electron emission device uses electron emission regions made from materials having low work functions or high aspect ratios. When exposed to an electric field in a vacuum atmosphere, electrons are easily emitted from these electron emission regions. Electron emission regions having a sharp front tip structure based on molybdenum (Mo) or silicon (Si) have been used. Also, electron emission regions including carbonaceous materials, such as carbon nanotubes, have been used.
Although the different types of electron emission devices have specific structures, they basically have first and second substrates sealed to each other to form a vacuum vessel, spacers arranged between the first and second substrates, electron emission regions formed on the first substrate, driving electrodes for controlling the emission of electrons from the electron emission regions, phosphor layers formed on a surface of the second substrate facing the first substrate, and an anode electrode for accelerating the electrons emitted from the electron emission regions toward the phosphor layers, thereby causing light emission to generate the display.
The spacers support the vacuum vessel to prevent it from being distorted and broken, and maintain a constant distance between the first and the second substrates. The spacers may be located corresponding to the non-light emission regions between the respective phosphor layers, such that they do not intercept electrons moving from the electron emission regions toward the phosphor layers.
However, in practice, given the practical trajectories of electron beams during the operation of the electron emission device, some of the electrons emitted from the electron emission regions do not move straight from the electron emission regions toward the phosphor layers at the corresponding pixels, but instead diffuse toward the non-light emission regions or toward incorrect phosphor layers at the pixels neighboring the target pixels.
These stray electrons may collide against the surfaces of the spacers, which, in turn, may develop an electrical charge, e.g., a positive potential or a negative potential, depending upon the spacer material. The surface-charged spacers may distort the trajectories of electron beams, resulting in a deterioration of display uniformity around the spacers and unintended light emission from the neighboring phosphor layers, resulting in an overall deterioration of screen image quality.